The use of water-occlusive and/or moisture-retentive dressings for treating skin wounds like pressure sores and ulcers of varied etiology is well widespread in the wound care field. These dressings are frequently a combination of a water-impervious and vapor-permeable membrane, which forms the outer surface of the dressing, with an absorbent core. The absorbent core typically comprises a polymeric foam, a fibrous hydrophilic polymeric material, a hydrogel, a matrix containing hydrocolloids, or combinations thereof. Dressings of this kind promote wound healing by providing a moist environment, while simultaneously removing excess of exudate and debris from the wound bed. Further, they serve as a barrier to protect the wound from outer contaminants and secondary bacterial colonization.
A drawback with certain materials employed as absorbent core is that when they are placed in direct contact with the wound for prolonged time, they may tend to develop adherence to the wound bed. This adherence is considered detrimental, since it usually leads to pain and damage of the newly formed wound tissue during dressing removal, eventually delaying healing. In order to minimize adherence, the use of low-adherent (or non-adherent) layers is a common practice. The low adherence refers to the adherence of the layer to the wound surface (not to the healthy skin). The low-adherent layer is sometimes present secured to the side of the dressing intended to lay proximal to the wound. Alternatively, a separated non-adherent layer component can be firstly positioned over the wound before the occlusive wound dressing comprising the absorbent core is applied. In both cases, the low-adherent layer advantageously contains openings to permit transport of wound fluid therethrough and into the absorbent core. The materials commonly described as low-adherent layers are for instance polymer films or fabrics (woven or non-woven), usually treated in a way to render them less adherent to the wound. Commercial products comprising non-adherent or low-adherent layers are e.g. Profore™ WCL (sold by Smith&Nephew), Mepitel® (sold by Mölnlycke Health Care).
With the aim of facilitating the application of the dressing to the wound site, and to hold them in position during use, the dressings often comprise an adhesive layer. The adhesive layer may be configured to cover the side of the wound dressing intended to lie over the wound during use. In this case, the adhesive layer favorably contains openings to permit passage of wound fluid from the wound bed into the absorbent core. The type of skin adhesive is suitably selected to have low-adherence to the wound, e.g. by selecting it to be hydrophobic, and thus making the use of additional low-adherent layers superfluous. U.S. Pat. No. 4,995,382 and EP 0 855 921 describe examples of such dressings. Alternatively, the adhesive layer can be configured to only contact the peri-wound skin of the wearer during use, and not the wound surface. In dressing constructions often referred as island dressings, the water-impervious backing layer extends beyond the edges of the absorbent core, and the adhesive layer is coated to the peripheral portion (border) of the backing layer, on the side intended to lie proximal to the healthy skin during dressing wearing. Such dressings are described e.g. in EP 1 303 239 and US 2009/124950. A low-adherent layer is sometimes advantageous in island dressings, as shown e.g. by the examples disclosed in U.S. Pat. No. 6,019,996.
The treatment of infected wounds, or wounds under risk of becoming infected, with non-woven or woven fabric dressings comprising an agent having some effect against microbial colonization is also known in the art. An infected wound is to be understood herein as a wound which has been entered and colonized by pathogenic microorganism like bacteria, fungi, protozoa and viruses. The non-woven or woven fabrics are usually made of natural or artificial fiber materials, or mixtures thereof, like e.g. cotton, cellulose and its derivatives, polyester, polypropylene or nylon. These wound dressings base their effect against microbial colonization in different mechanisms of action, depending on the fabric treatment. U.S. Pat. No. 4,617,326 describes a bacteria adsorbing composition comprising a woven or non-woven hydrophilic fabric, such as cotton fabric, which is treated chemically with a compound containing hydrophobic groups like dialkyl-carbamoyl chloride (DACC), especially dioctadecyl-carbamoyl chloride and dihexadecyl-carbamoyl chloride. It is proposed that when this product is applied to an infected wound, the microorganisms become bonded through hydrophobic interaction to the treated fabric and are eventually removed from the wound when the dressing is changed. Products of this kind are commercially available under the Cutimed® Sorbact (BSN medical) trademark. Alternatively, wound dressings of this kind can comprise an antimicrobial agent releasably or non-releasably incorporated into the fibers of the woven or non-woven fabric. The antimicrobial agent kills the microorganisms and/or inhibits the growth upon contact, either in the wound bed, in the exudate or inside the dressing. Some examples are contained in EP 2 253 336, WO 2007/120608, U.S. Pat. No. 6,087,549, WO 2006/121 935 and US 2002/177828. A large variety of efficient antimicrobial agents have been described in the art for this purpose, including biguanide salts like polyhexamethylbiguanide (PHMB), silver based compounds and quaternary ammonium salts, to name some.
The woven or non-woven fabric dressings with effect against microbial colonization are preferably directly applied to the wound in the form of a flat sheet, a pad, a ribbon or as several folded layers. The dressings should advantageously possess a reduced tendency to develop adherence to the wound bed. Due to their limited absorption capacity, often a secondary wound dressing comprising an absorbent core needs to be applied over the fabric material, in order to cope with the excess of wound exudate passing through it. Unitary multilayer laminate dressings are also known which combine in one article the woven or non-woven fabric layer with effect against microbial colonization, an absorbent core and optionally a water-impervious vapor-permeable backing membrane. Examples are described e.g. in U.S. Pat. No. 7,576,256 and US 2008/114279. In this prior art, the non-woven or woven fabric layer is non-detachably bonded to the absorbent core, to its surface which is proximal to the wound when the dressing is worn.
The non-woven or woven fabrics having effect against microbial colonization are ideally liquid permeable, low adherent and pliable. Disadvantageously, most of these fabrics are not significantly stretchable or expandable both in their length and width directions, corresponding to machine direction and cross direction during manufacture, showing practically absence of elasticity. As a consequence, when this fabric layer is bonded to the side of the absorbent core intended to lie proximal to the wound in a unitary dressing, at least the following drawbacks arise: a) most materials forming the absorption core, like e.g. hydrophilic foams, need to swell and expand to reach their maximum absorption capacity. When the fabric layer with reduced expansion capacity is bonded to the surface of the absorbent core, this causes the swelling of the absorbent core to be significantly restricted and its absorption capacity reduced; b) swelling of the absorbing core having bonded to its wound surface the fabric layer during absorption produces deformation and curling of the wound dressing, creating paths for wound contamination and cross-infection by external agents, and in the worst cases, leading to partial lost of contact between the dressing and the wound bed; and c) when an adhesive or a bonding layer is used to bond the fabric to the absorbent core, this layer is a source of additional costs and manufacturing complexity. Furthermore, the adhesive layer at least partially obstructs the fluid transport from the wound into the absorbent core, having a detrimental effect in the wicking capacity of wound fluids by the dressing.
From the above it is obvious that there is a need for an improved wound dressing which does not suffer from the drawbacks of the dressings known in the art, which is construed as an unitary dressing comprising an absorbent core and a non-woven or woven fabric on the wound proximal side of the absorbent core intended to lie proximal to the wound during use, and where the fabric comprises an agent having an effect against pathogenic microbial colonization of the wound.